Speaker
Nicholas Eidietis
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.107.pdf
DIII-D Research in Support of the ITER Disruption Mitigation System
N.W. Eidietis1, P. Aleynikov2, J. Herfindal3, E.M. Hollman4, A. Lvovskiy5, R.A. Moyer4, C.
Paz-Soldan1, D. Shiraki3
1
General Atomics, San Diego, USA
2
Max-Planck Institute for Plasma Physics, Greifswald, Germany
3
Oak Ridge National Laboratory, Oak Ridge, USA
4
University of California - San Diego, San Diego, USA
5
Oak Ridge Associated Universities, Oak Ridge, USA
Pioneering studies on DIII-D directly support the development and operation of the ITER
disruption mitigation system. Recent experiments examined the effects of SPI trajectory
orientation and the superposition of multiple SPIs upon mitigation metrics. In experiments,
the tangential SPI trajectory increases the current quench duration and halo current impulse
compared to a core-directed SPI trajectory. The degraded SPI performance due to the
change in injection trajectory implies ballistic transport, in addition to MHD mixing, is an
important aspect of SPI mitigation. The superposition of dual toroidally separated SPI is
also examined. It is found that when two differently sized pellets (10 torr-L and 400 torr-L)
are injected into the plasma simultaneously, the radiation fraction measured near the
injector ports is reduced, the current quench duration increases, and the plasma cooling
duration decreases relative to injection of the single 400 torr-L pellet, indicating a
degradation in the effectiveness of mitigation. Examination of the runaway electron (RE)
energy distribution function evolution in the flattop of low-density, Ohmically driven
discharges using MeV-scale bremsstrahlung emission provides direct comparison to
theoretical models of RE evolution. The observed energy spectra display the predicted
energy “bump” indicating the energy attractor predicted by theory, as well as the motion of
the bump in energy space as the collisionality (density) is varied. Measured spectra also
exhibit a strong dependence of the high-energy tail upon the synchrotron force (varied
using Bt) in qualitative agreement with theory. A novel shell pellet technology has been
installed on DIII-D to study the deposition of impurities in the core without significantly
cooling the edge, and recent experimental results are discussed.
* This material is based upon work supported by the U.S. Department of Energy, Office of
Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a
DOE Office of Science user facility, under Award DE-FC02-04ER54698.
